New to Diesel - Can't get 85 300TD to start! - PeachParts Mercedes-Benz Forum

Codifex Maximus · #1 02-09-2010, 06:02 PM

Yep. Sounds like either a dead or dying battery, no charge on the battery, and possibly a fault in the charging circuit. As suggested, verify all grounds are free of corrosion and are tight. Check for loose belts.

hankthoreau · #2 02-09-2010, 06:11 PM

Ok, so I read the whole thread, and I am stuck here in the EXACT position, a half hour away from picking up my son at school (my mom's on her way) and I am FURIOUS!

Basically, same issue... mine's a 1983 300TD Wagon... have had issues over the past month every few days... I get in, and turns over once or twice slowly, then nothing. NOW, after fiddling with the antenna all day, got it working (well, receiving reception... unplugged it), went to start it up and nothing but this f***ing buzzing from the GP relay box. First time for the buzz. I've jumpstarted it in the past and it ran fine the rest of the time, until randomly, would not start. Tested voltage with everything off at battery... 12.6 or something like that. Turned key on, drops to 7.5ish. Not sure if that's normal. My radios actin' all crazy... dim lights and ****... like there's a cross somewhere, but I'm almost positive there is NOT...

Low voltage would be caused by faulty voltage regulator? Or does that only function when running? Or faulty alternator? or battery? I bought a new one 14 months ago. Just don't get it and am frustrated....

No loose cables or belts... just up and started getting testy on me.

Leavin' it to the pros on this forum... y'all are way too smart to let this one stump you.

Codifex Maximus · #3 02-09-2010, 06:19 PM

Hank,

Take your battery out and put it on a trickle charger. See if that fixes the issue for a while - till it goes dead again maybe. If it does go dead after a while then you've got an issue with your charging.

Also, those ground connection issues seem to keep popping up with posters. Check em out and make sure they are clean and tight.

hankthoreau · #4 02-09-2010, 06:22 PM

Thanks for the quick response...

(1) Exactly which ground connections should be confirmed as tight?

(2) I was reading more, and found that the voltage at the battery posts when running should be 13.5-14.0, and 12.7 fully charged... when it was running last week, it measured 13.6... today, right now, it is at 12.5. When I turn the key, it drops to 7.5. Is that normal?

Thank you thank you thank you....

hankthoreau · #5 02-09-2010, 06:31 PM

Also... the buzzing starts within 2 seconds of turning the ignition on... all gauges act normal, except the tachometer spins up to 6000rpm and coincides with the buzzing from the GP relay....

hankthoreau · #6 02-09-2010, 07:31 PM

Put the battery in my bicycle basket and headed to the battery specialists... they told me it was from 2002... YAH... THAT'S WHAT I SAID................

So, turns out the 'out of the way' mechanic installed a 7 year old battery as new to me last year...

He is no longer in business according to the phone message.

Replace the battery...

Does it start?

To Be Continued....

hankthoreau · #7 02-09-2010, 10:34 PM

And YES.... as a matter of fact, it started better than EVER... less than one crank, I swear.

MANY BLESSINGS TO THIS FORUM AND EVERYONE INVOLVED IN POSTING THE THREADS I READ TO COME TO GRIPS WITH THE STUPIDITY OF OTHERS!

Replace that battery... your Benz will love you.

Codifex Maximus · #8 02-09-2010, 07:35 PM

Electrically, a battery acts like a constant voltage machine. Current should be able to vary alot while voltage remains nearly the same.

Inside every battery is an effective resistance to the flow of electricity which forms in the series circuit of the battery. As the battery discharges, the resistance increases lowering the voltage developed across the output terminals under heavy load. Now, this resistance is not a real resistor but an effect. When the resistance reaches infinity, the battery is totally dead.

Just recharge it on a trickle charger. That *should* get you going but the original problem likely remains. Most likely a faulty charging circuit.

Edit: I'd see if that battery will hold a charge before replacing it.